Doering: Lepyronia quadrangularis. 563 



DEVELOPMENT OF THE CiENITALIA. 



As early as the third iiistar the iiyinphul genitalia arc not only 

 distinctly visible, but furnish irliablc characters l)y which to dis- 

 tinguish the sexes. They cannot be clearly made out, however, in 

 the first two stages without careful study. 



The male genitalia arise from a genital area on the ninth abdom- 

 inal segment. In the first and second instars only one pair of 

 valves is present. Superficially they appear as two opaque, elongate, 

 elevated ridges which occupy the major part of the ninth sternite. 

 Closer examination reveals that they are two chitinous pockets 

 (pi. LXI, fig. 11, which are separated from each other by a median 

 chitinous band and which produce the genital appendages of the 

 next nymphal stage. The pockets are attached to the caudal border 

 of the genital area with their apices directed caudad and are 

 rounded at the tip. The genital area is comparatively short and 

 extends cephalad under the caudal margin of the eighth sternum, 

 due to the telescopic arrangement of the abdominal segments, so 

 that at first glance the pockets appear to arise from the eighth 

 sternite. This pair of pockets produces the genital plates of the 

 adult. 



In the second instar (fig. 2 I the pockets have increased slightly 

 in size, but are similar in other respects to those of the first. 



In the third instar there is a noticeable increase in size of the 

 genital area. The pockets of the genital plates have become broader 

 but are not so deeply bilobed. In addition to the one pair of pockets 

 there is now present another pair, which are located dorsad and 

 slightly caudad of the first pair. These produce the genital styles 

 or claspers of the adult insect. 



In the fourth instar the genital area has become large and promi- 

 nent. There is a great increase in the size of the dorsal pockets, 

 which have now become twice as long as the ventral pair. Both 

 are rounded at the tip. 



In the fifth instar still greater changes have taken place. The 

 ventral pockets have become greatly elongated and their apices have 

 diverged slightly. The genital area has lengthened between the 

 ventral plates and the dorsal plates so that the former do not ex- 

 tend over the latter at all. The dorsal pockets have also diverged 

 considerably, and between them can be seen the apices of another 

 pair of pockets. These median pockets are only half as long as the 

 pockets of the genital styles, are rounded at the apex and produce 

 the (I'dagus of the adult. 



